Cable bolts are steel tendons inserted into bore holes in a rock surface to stabilize the rock surface against collapse. In hardrock mining, the whole length of the tendon is grouted, and a plate is attached to the tendon adjacent to the rock surface. The tendon is then stressed; the plate bears upon the rock surface and thereby stabilizes the rock surface.
Tendons typically comprise a plurality of steel strands wound together to form the tendon. It is known to provide multi-stand cable bolts that are formed with bulbs or expanded portions in order to increase the surface area of the tendon in contact with the grout to more securely embed the tendon in the grout. The bulbs or expanded portions thus increase the radial confinement of the tendon within the borehole.
In coal mining, where any movement of the rock surface is undesirable, an end portion of the tendon disposed innermost in the bore hole is secured therein by spinning the end portion in resin, attaching a resin dam to an opposing end of the spun end portion, and allowing the resin to cure. The remaining portion of the tendon disposed in the borehole is then tensioned to immediately stabilize the rock surface. The bore hole can then be grouted safely a short time later. In the meantime, the rock surface is stabilized against collapse before grouting commences or during the grout curing period.
When multi-strand cable bolts provided with bulbs or expanded portions are used to stabilize a rock surface of a coal mine, as described above, the bulbs or expanded portions tend to collapse under the load placed on the cable bolt when the tendon is tensioned to stabilize the rock surface. This type of multi-strand cable bolt is thus rendered ineffective as an anchoring means for coal mine rock surfaces, as the collapsed bulbs do not afford sufficient surface area to bond with the grout and the tendon “stretches” or lengthens as the bulbs collapse.
The present invention attempts to overcome at least in part some of the aforementioned disadvantages.